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Injection-blow molding apparatus with parison heat redistribution means |
| 3963399 |
Injection-blow molding apparatus with parison heat redistribution means
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| Patent Drawings: | |
| Inventor: |
Zavasnik |
| Date Issued: |
June 15, 1976 |
| Application: |
05/373,358 |
| Filed: |
June 25, 1973 |
| Inventors: |
Zavasnik; Fred J. (Bolingbrook, IL)
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| Assignee: |
Continental Can Company, Inc. (New York, NY) |
| Primary Examiner: |
Husar; Francis S. |
| Assistant Examiner: |
Rowold; Carl |
| Attorney Or Agent: |
Shapiro; PaulKerwin; Joseph E.Dittman; William A. |
| U.S. Class: |
425/526; 425/529 |
| Field Of Search: |
425/242B; 425/326BJ; 425/DIG.208; 425/DIG.209; 425/DIG.213; 425/324B; 425/387B; 264/94 |
| International Class: |
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| U.S Patent Documents: |
2331687; 3191225; 3364520; 3412186; 3433862; 3584337; 3609803; 3667887; 3690802; 3694124; 3707591; 3740180; 3878282 |
| Foreign Patent Documents: |
2,059,917 |
| Other References: |
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| Abstract: |
Method and apparatus for molding plastic articles by forming a parison on a core within an injection mold, cooling the internal and external walls of the parison thus formed by heat transfer through the core and the injection mold, transferring said core to a delay position for permitting redistribution of heat from the interior of the parison to the exposed walls to obtain a more uniform temperature just above the material's glass transition temperature, and subsequently transferring said core to an expansion mold for expanding same, the cooling and heat redistribution permitting a greater degree of orientation of the polymer chains of the formed articles. Preferably, the apparatus for practicing the process includes injection and expansion molds supported in such a relation as to permit a substantial time interval between injection and expansion of the parison. |
| Claim: |
I claim:
1. Apparatus for forming a biaxially oriented container comprising:
a. support means carrying an injection and expansion mold, said molds being opposite one another, said injection and expansion molds having fluid passages therein for circulating fluid to cool the exterior walls of a parison formed in said moldto a first temperature, and
b. core support means operatively associated with said support means carrying at least four cores radially extending from the support means at 90.degree. intervals and for indexing said cores sequentially to the injection mold, a delay position,the expansion mold and to an ejection station, said cores having fluid passages therein for circulating fluid to cool the interior walls of said parison to a second temperature higher than the first temperature.
2. An apparatus for forming a biaxially oriented hollow article comprising the combination of:
a. support means carrying an injection mold and an expansion mold, said injection mold having a fluid cooling passage therein for circulating a fluid at a first temperature;
b. core support means operatively associated with said support means carrying a core for sequentially indexing the core in juxtaposition with the injection and expansion molds and the core having a fluid cooling passage for circulating a fluid ata second temperature higher than the first temperature and the core support having fluid expansion passages therein for cooling and expanding a parison; and
c. means operatively associated with said support means to index the parison to and maintain the parison at a time delay station to permit the parison formed on said core to redistribute its heat from the interior of the parison throughout theparison prior to indexing the core into juxtaposition with the expansion mold. |
| Description: |
BACKGROUND OF THE INVENTION
This invention relates to the field of injection blow molding. More specifically, it relates to a method and apparatus for obtaining a higher degree of biaxial orientation of articles made by such processes, and may have application in the fieldof either blow molding or vacuum molding. Prior designs for injection blow molding machines have primarily related to designs in which minimum machine cycle time could be obtained. For example, U.S. Pat. No. 2,853,736 teaches the formation of aparison at a first injection station and immediate transfer thereof to a second station at which they are blown to desired configuration with subsequent ejection of the blown article at a third station. While such apparatus may be sufficient andeconomical for the manufacture of many articles, they are not believed to result in a high strength, oriented article such as a bottle suitable for containing pressurized liquids or beverages.
Further, U.S. Pat. No. 3,492,387 suggests that a thermoplastic material may be injected into an injection mold; that the slug of thermoplastic material is to be held in the mold for a time period of four seconds to permit cooling, withsubsequent expansion of the thermoplastic slug by mechanical means; such procedures intended to result in a more highly oriented hollow article. Finally, U.S. Pat. No. 3,311,684 suggests that a parison may be extruded, with the interior walls of saidparison being cooled by a fluid, followed by stretching of the parison in vertical and in radial directions so as to obtain the desired biaxial orientation.
Although U.S. Pat. No. 3,492,387 teaches orientation, it is not believed that the apparatus is best suited for the formation of containers for pressurized liquids or achieves the desired strength. Alternatively, U.S. Pat. No. 3,311,684involves an extrusion process with its resulting waste, and does not seemingly provide for uniform heat distribution within the parison whereby maximum orientation can be achieved.
SUMMARY OF THE INVENTION
In order to overcome these disadvantages and to produce a container having a high degree of biaxial orientation of the polymeric chains of the thermoplastic material, and to provide a container suitable for holding pressurized liquids, theinstant process and apparatus for practicing same first utilizes an injection process in which a thermoplastic material is injected into an injection mold about a core, with subsequent cooling of the internal and external surface walls of the parisonthus formed. Inasmuch as such cooling primarily takes place at or near these surfaces, the entire parison is not reduced to a temperature just about its glass transition temperature (T.sub.G) such that maximum orientation of the article can be achieved. Accordingly, this invention includes an additional step of tranferring the parison to a holding station whereby the heat within the parison interior may be redistributed to achieve a more uniform temperature (just above T.sub.G for the material)throughout a cross-section of the parison wall with subsequent expansion thereof so as to more completely align the polymeric chains. Too, such expansion process also includes the utilization of a mold having substantial heat transfer capabilitieswhereby the biaxial orientation may be "frozen into" the formed article. Similarly, the apparatus of the instant invention includes a core carrier, and an injection and expansion mold so arranged at station locations that a holding cycle or stationexists between the forming step and the expansion step. Such arrangement is capable of permitting the formation of oriented containers at the highest possible production rate.
Accordingly, it is an object of the instant invention to provide a process for manufacturing hollow articles suitable for containing pressurized liquids. Too, it is a further object of the instant invention to provide a process whereby themaximum biaxial orientation of hollow articles may be obtained and to utilize the inherent heat conduction properties of thermoplastic so as to obtain a parison having more uniform temperature throughout its cross-section for this purpose. Finally,apparatus is suggested whereby such orientation may be accomplished without reducing the production rate of the formed containers so as to permit an economical process.
DESCRIPTION OF THE DRAWINGS
The manner in which the objects of the invention are attained will be made clear by a consideration of the following specification and claims when taken in conjunction with the drawings in which:
FIG. 1 is a side elevational view of the apparatus which may be utilized in practicing the instant process;
FIG. 2 is a top view of a turntable which is utilized to carry the cores on which the parison are formed; and
FIG. 3 is an elevational view partially in section of a core utilized in practicing the instant invention.
DETAILED DISCUSSION
As previously indicated, the instant invention includes the injection of a thermoplastic material about a core within an injection mold to form a parison and subsequent heat transfer from the parison's exposed walls to a fluid circulating withina core and the injection mold. Subsequently, the parison is transferred to a holding station whereby heat redistribution within the parison results in a more uniform parison cross-section temperature just above its glass transition temperature. Then,the parison is transferred to an expansion mold whereby a fluid energy is exerted against the interior wall of the parison causing same to expand against the cavity walls to form a completed article. Too, by controlling the temperature within theexpansion mold, the orientation of the polymer chain is "locked in".
The instant process will enhance the orientation of the polymeric chains of most thermoplastic resins used for injection mold applications. However, preferred resins are those of thermoplastic polymers having a high nitrile monomer content inthe order of 60% or more such as the copolymers of olefinically unsaturated nitriles such as acrylonitrile, methacrylonitrile and ethylenically unsaturated comonomers such as alkyl acrylates, styrene and graft copolymers of the nitrile copolymers withdiene rubbers.
The process is generally indicated in FIGS. 1 and 2 which depict a parison 5 being injected through nozzle 4 of an extruder (not shown) into an injection mold 15 about a core 52 at station A. Preferably, four such cores 52 are carried byturntable 40 by radially extending arms 42 at 90 degree intervals. After the parison 5 is formed in the injection mold, it is held in such position for approximately four or five seconds to permit cooling of the material adjacent external and internalwalls 7 and 8 (see FIG. 3), after which time the turntable 40 is rotated 90.degree. to a cooling station B. At this station, heat transfer from the interior 9 of the parison to the surface walls 7 and 8 may be effected. After the temperature throughouta cross-section of the parison wall is permitted to become more uniform, the turntable 40 will again be rotated another 90 degrees to station C in juxtaposition with the expansion mold 25. This mold is then closed, with air being emitted through thecore 52 to expand the parison against the cavity walls thereof which are cooled by the passage of fluid therethrough so as to lock in the orientation. The core is then indexed on the turntable 40 another 90 degrees to an ejection station D at whichpoint, ejection means 32 will strip the formed article from the core.
FIG. 1 indicates appropriate movement of the turntable. This side elevational view depicts the turntable 40 as being supported for both vertical and rotational movement, and appropriate motors for accomplishing such movement are well known inthe art. Specifically, U.S. Pat. No. 3,100,913 which issued to De Matteo on Aug. 20, 1963 depicts one such arrangement. The lower mold halves 17 and 27 of the injection mold and the blow mold are carried by a support 11, while the upper mold halves16 and 26 are moved vertically as indicated by hydraulic motors (not shown). Prior to indexing the table 40 by an appropriate motor (not shown) the upper mold halves 16 and 26 must be moved to the dotted line position, while the turntable is elevatedslightly by a motor (not shown) so as to permit the parison 5 in the injection mold 15 and the formed article 6 in the expansion mold 25 to clear the lower mold halves at which time, rotation is effected.
Thus in operation, the molds 15 and 25 are initially open, and the turntable 40 is rotated so as to align two of the cores 52 in juxtaposition with the molds 15 and 25. Simultaneously, the turntable 40 and the upper mold halves 16 and 26 arelowered with two of the cores 52 resting in the lower mold halves with the upper mold halves closing over them. Accordingly, injection and expansion will take place in these two molds 15 and 25 while cooling of another parison and ejection of a formedarticle occurs at the other cores 52. Subsequently, the upper mold halves are opened with the turntable rising sufficiently to clear the lower mold halves and indexing again is effected.
Thus, in considering FIGS. 1 and 2 together, it should be apparent that the turntable 40 will successively rotate each of the cores 52 to the injection mold 15, the holding station B, the blow mold 25, and the bottle ejection station D. Too, itshould also be apparent that the time lapse which occurs at the cooling station is substantially equal to the time for closing the molds 15, injecting a thermoplastic material into same, the cooling time permitted in the injection mold and the timerequired for rotation. By providing such additional cooling period at station B, redistribution of heat within the parison walls will be affected as more fully described hereinafter.
In order to maximize the production rate of formed articles, rapid and uniform cooling of the parison is desired. Accordingly, substantial cooling of the interior and exterior walls 7 and 8 of the parison 5 is obtained within the injection mold,with the uniformity occurring as a result of heat redistribution at the cooling station B.
As shown in FIG. 1, the exterior wall 7 of the parison may be cooled through the utilization of cooling passages 20 within the injection mold, which are well known in the art. Thus, fluid may be directed through conduits 18, passages 20 andexhausted from the opposite end of the injection mold by conduits 19.
FIG. 3 depicts structure for the cores 52 which may be utilized to cool the interior wall 8 of the parison. The radial arm 42 mounted on turntable 40 carries the cylindrical core 52 as shown. Extending through the arm 42 and the core 52 is abore 57 which carries a control rod 54. As depicted, the control rod is a cylindrical member having at its forward end a conical end section 58 which sealingly engages a conical counter bore 53 on the end of the core 52. Within the arm 42 is a counterbore 68, into which the control rod 54 extends and is threadedly engaged with an annular sealing member 72. A spring 76 interposed between the sealing member 72 and the end of the counter bore 68 urges the control rod 54 to the rear or left as viewed inthe drawing.
As previously indicated, heat is to be transferred from the interior wall 8 of the parison, through the core 52 by the utilization of fluid passages. Such fluid passages may take the form of double threads 56 located 180 degrees apart on theexterior wall of the control rod 54. Accordingly, fluid may be entered through a bore 51 in the arm 42 and travel through one of the threaded grooves to the forward end of the control member and return through the opposite groove and out an aperture 50on the opposite side thereof. Appropriate seals as shown on the opposite ends of the control rod may be used to effectively preclude the leakage of fluid from the core.
In order to cause expansion of a parison previously formed on the core 52 within the blow mold, a bore 59 is formed within the control rod 54. At the forward end of the control rod is a cross drill 60 which permits air flowing into the bore 59to pass between the surfaces formed by the end section 58 and conical bore 53 when the control member is urged forward. Such air is admitted to the bore via an aperture 61 in arm 42 and cross drill 62 within control member 54. As is well known in theart, camming means may be utilized to urge the control member 54 forward at the appropriate time so as to emit air to the interior of the parison and expand same against the walls of the expansion mold.
MODE OF OPERATION
Assuming that a core 52 has been rotated in juxtaposition the injection mold 15 with this mold being subsequently closed, a thermoplastic material may be injected into the mold about the core through the nozzle 4. The time period for injectionand the holding of pressure within the injection mold may take three of four seconds. Subsequently, the nozzle 4 is retracted in the conventional manner and the surfaces 7 and 8 of the parison are then cooled for several additional seconds. Ideally, itis contemplated that the surface of the core 52 should be maintained at the glass transition with the injection mold being maintained at a lower temperature through heat transfer to fluid passing through the core 5 and the injection mold 15. Thus,during the delay period within the injection mold, the interior 7 and exterior 8 walls of the parison and the thermoplastic adjacent thereto are rapidly cooled to or below an orientation temperature. (Due to the high thermal conductivity of the metalcore and injection mold, the surfaces 7 and 8 are believed to achieve substantially the same temperature as those metal components.) With respect to the cooled surface walls, the interior 9 may be regarded as a heat reservoir.
Subsequently, the upper mold half is opened, the turntable 40 raised and rotated as previously indicated so as to move the cores 52 and formed parison 5 to a holding station B. At this holding station, heat will continue to flow from the interiorwall 8 of the parison through the core 52 and the thermoplastic material in this region will be reduced to a point just above its glass transition temperature. Simultaneously, however, heat will flow from the interior 9 of the parison outwardly so as toreheat the exterior wall 7 of the parison to a point just above its glass transition temperature. Accordingly, this heat transfer process results in a more uniform temperature of the cross-section of the parison wall in a minimum amount of time. Fromthe holding station B, the parison is indexed to the blow mold for expansion, such being affected by the delivery of air through the bore 61 of the arm 42, into the cross drill 62, bore 59, cross drill 60 and out of the end of the core the forwardmovement of the control rod being affected by cams (not shown) so as to open the seal effected between the surfaces of the counter bore 53 and the conical end 58 of the control member. Simultaneously with such expansion, the expanded article will becooled by fluids passing through passages 29 within the expansion mold 45 so as to freeze or lock in the orientation of the polymer chains. Subsequent opening of the mold 45 and rotation of the turntable will move the formed article on its core to anejection station at which point the bottle or container may be removed.
As contemplated, it is anticipated that during each of the four cycles, or one complete revolution of the turntable, four complete articles will be made. As viewed in FIG. 1, it is also anticipated that several molds may be vertically stackedone upon the other, or they may be placed side by side so as to increase the maximum rate of production.
EXAMPLE
Containers fabricated from Barex 210 a commercially available amorphous thermoplastic nitrile resin consisting of acrylonitrile/methylacrylate-acrylonitrile/butydiene graft copolymer containing about 69% acrylonitrile, 22% methylacrylate, and 9%butadiene rubber were formed through the process herein identified. This resin has a glass transition temperature of approximately 180.degree.F, and was injected into an expansion mold of the type illustrated in FIG. 1 in a plasticized state, at atemperature of approximately 390.degree.F. The fluid passing through the injection mold 15 was maintained at a temperature of 120.degree.F while a coolant within the blow stick 52 was maintained at approximately 200.degree.F, approximately 20.degree.Fabove the glass transition temperature of Barex 210. The extruder device injected and held a pressure within the injection mold 15 for a period of three seconds, while cooling of the parison against the surfaces of the core and the injection moldcontinued for an additional 4 seconds. The core was then transferred to a holding station, with a total delay time (including time for movement of the core and time at station B) of twelve seconds before actual blowing of the container within a blowmold having a coolant passing therethrough at a temperature of 52.degree.F.
The test bottles (at a weight of approximately 33.7 grams and having a volumetric capacity of approximately 317 cc) were then filled with a commercial carbonated soft drink, charged with CO.sub.2 to a pressure of 75 PSI absolute at 72.degree.Fand then stored at 100.degree.F and 80% relative humidity for 2 weeks.
The volume expansion or creep of the test bottles was then determined by placing the bottles in a container of water with a fixed filling level. The volume of water displaced by the test bottles at the end of the period in excess of thatdisplaced at the beginning of the period is a measure of the volume expansion which occurred during the 2 weeks' storage time. It was determined by this creep test that the average volume expansion of the bottles made as indicated in this example was9.01% of the original volume.
Accordingly, applicant is proferred herein an apparatus and a process for obtaining a thermoplastic container having a high resistance to creep and deformation under pressure. In the above example, the interior wall of the parison was directlycooled to a point just above its glass transition temperature while the exterior wall is cooled below the point and subsequently reheated by heat transfer. However, both surfaces might be reduced below the glass transition temperature and subsequentlyreheated during the "cooling" or delay cycle and such general procedure represents a most economical and rapid manner by which a thermoplastic material may be reduced from its injection temperature to a more uniform orientation temperature. It ispreferred that this more uniform temperature at which expansion occurs be within a 50.degree.F range above T.sub.G.
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